1. Field of the Invention
The present invention relates to a rolling bearing for a rocker arm, said rolling bearing comprising an at least partly circular outer part, an at least partly circular inner part and a number of rolling elements which are fitted between the outer part and the inner part.
The invention also relates to the use of such a rolling bearing in a roller mill for grinding of particulate material, such as cement raw materials, cement clinker and similar materials, with said roller mill comprising a substantially horizontal grinding table and a roller set capable of revolving about a vertical shaft, said roller set comprising a number of rollers rotating about respective roller shafts which are connected to the vertical shaft via a hinged connection allowing a free circular movement of the roller up and down in a plane including the centreline of the roller shaft, and said roller set being configured for interactive operation with the grinding table.
The rolling bearing according to the invention may be used in any context where it is essential that a rocker arm or shaft has the capability to move back and forth at relatively small angular rotations, and, therefore, it is particularly suitable for use in connection with the hinged connection in roller mills of the aforementioned known kind.
2. Background of the Art
In the known roller mills, the hinged connection which connects the roller shaft with the vertical shaft is typically made up of a traditional slide bearing which may be lubricated by means of a suitable lubricant. It is the function of the hinged connection to ensure that the rollers, independently of one another, have the ability to follow the height variations of the material bed deposited on the grinding table during the operation of the mill. With respect to direction and size, the force which is to be absorbed by the hinged connection is virtually constant relative to the bearing journal the angular rotation of which is generated by the variations in the thickness of the material bed, and typically maintained within an interval of ±0.5 to 5 degrees. The frequency of the angular rotation of the bearing journal will typically be within the interval of 0.5 to 1 Hz. If the known roller mill is used for grinding of particulate material, such as cement raw materials, cement clinker and similar materials, the hinged connection will be subjected to a relatively high pressure which, due to frictional forces between the parts of the hinged connection, will give rise to undesirable heat generation not immediately reducible by means of a lubricant because of the unilateral constant stress loading and the very small angular rotations back and forth of the bearing journal will not be sufficient to draw the lubricant into the zone of loading. Of other commercially available bearing types mention can be made of a hydrodynamic slide bearing which cannot be used since there is no continuous rotation of the bearing journal, hence preventing the formation of a hydrodynamic lubricating film, as well as a hydrostatic radial bearing which from a technical viewpoint is a perfect bearing solution which gives full support both in the static condition and subject to rotation, but its drawback is that it is too complicated, sensitive and expensive. Nor are traditional rolling bearings comprising an outer and an inner ring and circular-cylindrical rollers fitted in between deemed to be suitable for the purpose, partly because the small angular rotations will not allow the rollers to draw lubricant into the loading zone and partly because the circular-cylindrical form of the rollers only make it possible to incorporate a limited number of supporting rollers in the bearing, resulting in a significant load rate on each supporting roller. So, the fact remains that none of the traditional, commercially available bearing types are deemed to be directly suitable for the described load condition without giving rise to significant disadvantages.